1. Field of the Invention
The present invention relates to multiplex transmission apparatuses for optically transmitting a plurality of signals and, more specifically, to a multiplex transmission apparatus that converts a plurality of the same or similar signals varied in phase into optical signals and multiplexes these signals for transmission through a single optical fiber.
2. Description of the Background Art
FIG. 15 is a block diagram showing the structure of a conventional multiplex transmission apparatus. In FIG. 15, the multiplex transmission apparatus includes first and second multiplexers 15011 and 15012, first and second optical transmitters 15021 and 15022, an optical multiplexer 1503, an optical transmission path 1504, an optical separator 1505, first and second optical receivers 15061 and 15062, a delay controller 1507, and a multiplexer 1508.
The operation of the above structured multiplex transmission apparatus is described. The first and second multiplexers 15011 and 15012 each multiplex a plurality of electrical signals externally supplied (for example, RF signals received by an antenna), and then outputs the resultant signal.
Assume herein that the electrical signals supplied to the first and second multiplexers 15011 and 15012 are equal in signal parameter such as frequency, modulation scheme and modulation information, but different in phase. One example of such signals are those outputted from the same signal source but having different phases because they respectively reached the first and second multiplexers 15011 and 15012 at different times.
In FIG. 15, the first and second multiplexers 15011 and 15012 are each supplied with two electrical signals. The first multiplexer 15011 is supplied with a first signal (hereinafter, first main element signal) Sa having a frequency fa and a phase angle 0 and a second signal (hereinafter, second main element signal) Sb having a frequency fb and a phase angle 0. The second multiplexer 15012 is supplied with a first signal (hereinafter, first sub-element signal) Sa having the frequency fa and a phase angle+xcfx841 (phase delayed by xcfx841) and a second signal (hereinafter, second sub-element signal) Sb having the frequency fb and a phase anglexe2x88x92xcfx842 (representing phase advanced by xcfx842). Note that the first main element signal and the first sub-element signal are hereinafter collectively referred to as first element signals, while the second main element signal and the second sub-element signal are as second element signals.
In FIG. 15, the above signals are represented as follows: the first main element signal as Sa@fa(0), the second main element signal as Sb@fb(0), the first sub-element signal as Sa@fa(xcfx84a), and the second sub-element signal as Sb@fb(xcfx84b). The mark xe2x80x9c@xe2x80x9d is an identification mark with a signal name placed therebefore and signal parameters placed thereafter for indicating attributes. Placed as the signal parameters are the frequency and the phase angle, which is enclosed in parentheses.
Note that the above phase angles can be converted into propagation delay times, and therefore are treated herein as equivalent thereto. Also, the first and second main element signals are hereinafter collectively referred to as a main signal group, while the first and second sub-element signals are as a sub-signal group.
The first optical transmitter 15021, provided correspondingly to the first multiplexer 15011, converts the main signal group outputted from the first multiplexer 15011 into a first optical signal having a wavelength xcex1. Similarly, the second optical transmitter 15022, provided correspondingly to the second multiplexer 15012, converts the sub-signal group outputted from the second multiplexer 15012 into a second optical signal having a wavelength xcex2.
The optical multiplexer 1503 multiplexes the optical signals outputted from the first and second optical transmitters 15021 and 15022, and sends out the resultant optical signal to the optical transmission path 1504. The optical separator 1505 separates the optical signal coming through the optical transmission path 1504 into two, based on the wavelength. The separated optical signals are outputted as a first optical signal having the wavelength xcex1 and a second optical signal having the wavelength xcex2.
The first optical receiver 15061 is supplied with the first optical signal outputted from the optical separator 1505. The first optical receiver 15061 converts the supplied first optical signal into an electrical signal (main signal group) through square-law detection. Similarly, the second optical receiver 15062 is supplied with the second optical signal outputted from the optical separator 1505. The second optical receiver 15062 converts the supplied second optical signal into an electrical signal (sub-signal group) through square-law detection.
The delay controller 1507 gives a predetermined time delay xcfx84x to the main signal group outputted from the first optical receiver 15061, and then outputs the main signal group. The multiplexer 1508 multiplexes the main signal group with the time delay given thereto outputted from the delay controller 1507 and the sub-signal group outputted from the second optical receiver 15062, and then outputs the resultant signal.
For the above structured multiplex transmission apparatus, how to set the time delay xcfx84x in the delay controller 1507, and the operational principle and effects of the apparatus in terms of setting the time delay are described below by using an example.
FIG. 16 is one example of application of the present apparatus, schematically illustrating the structure of a receiving system using a phased array antenna. In FIG. 16, the system includes first and second antenna elements 16011 and 16012, first and second transmission paths 16041 and 16042, a delay controller 1507, and a multiplexer 1508.
Here, the first and second antenna elements 16011 and 16012 in FIG. 16 correspond to the first and second multiplexers 15011 and 15012 in FIG. 15, respectively. Also, the first and second transmission paths 16041 and 16042 in FIG. 16 schematically correspond to a propagation path from the first optical transmitter 15021 to the first optical receiver 15061 and a propagation path from the second optical transmitter 15022 to the second optical receiver 15062, respectively. The delay controller 1507 and the multiplexer 1508 in FIGS. 15 and 16 are the same in structure, and therefore provided with the same reference numerals.
The first antenna element 16011 in FIG. 16 is supplied with signals similar to the first main element signal and the second main element signal supplied to the first multiplexer 15011 in FIG. 15. The second antenna element 16012 in FIG. 16 is supplied with signals similar to the second main element signal and the second sub-element signal supplied to the second multiplexer 15012 in FIG. 15. In other words, the first main element signal and the first sub-element signal are the same signal outputted from the same signal source, but different in phase due to a positional relation among the signal source and the first and second antenna elements 16011 and 16012. The same goes for the second main element signal and the second sub-element signal.
For example, the first main element signal supplied to the first antenna element 16011 is the first element signal Sa, and so is the first sub-element signal supplied to the second antenna element 16012. However, the first sub-element signal passes through a propagation path longer than that of the first main element signal, and therefore is delayed in phase by the amount corresponding to the propagation time difference+xcfx84a.
On the other hand, the second main element signal supplied to the first antenna element 16012 is the second element signal Sb, and so is the second sub-element signal supplied to the second antenna element 16012. However, the second sub-element signal passes through a propagation path shorter than that of the second main element signal, and therefore is advanced in phase by the amount corresponding to the propagation time differencexe2x88x92xcfx84b.
The element signals supplied to the first and second antenna elements 16011 and 16012 are multiplexed together, propagated through the corresponding first and second transmission paths 16021 and 16022, and then multiplexed by the multiplexer 1508.
Here, according to principles governing this receiving system, in a case where two signals equal in signal parameter such as frequency, modulation scheme, and modulation information are multiplexed together, the resultant signal has an amplitude double the amplitude of these signals if they are equal in phase. On the other hand, if these two signals are different in phase, both signals are cancelled out, and the signal level after multiplexing becomes lower or none.
Since the system shown in FIG. 16 (or the apparatus shown in FIG. 15) follows the above principles, the delay controller 1507 is inserted into the first transmission path 1604, giving the time delay xcfx84x. By adjusting the time delay xcfx84x, the system can selectively output the first or second element signal from the multiplexer 1508.
For example, the time delay xcfx84x is so adjusted as to coincide with the propagation time difference+xcfx84a of the first sub-element signal supplied to the second multiplexer 15012 (or the second antenna element 16012) with reference to the first main element signal supplied to the first multiplexer 15011 (or the first antenna element 16011). Thus, the system can selectively output the first element signal. Alternatively, the time delay xcfx84x is so adjusted as to coincide with the propagation time differencexe2x88x92xcfx84b of the second sub-element signal supplied to the second multiplexer 15012 (or the second antenna element 16012) with reference to the second main element signal supplied to the first multiplexer 15011 (or the first antenna element 16011). Thus, the system can selectively output the second element signal.
Note that the number of multiplexers (or antenna elements) is not restricted to two, and may be more, as required. In such case, the transmission path and the delay controller are required as many as the multiplexers or the antenna elements.
As stated above, in the conventional multiplex transmission apparatus, signal groups including a plurality of element signals varied in phase are transmitted through a plurality of paths corresponding to the signal groups, and then multiplexed together for output. In such structure, the propagation time of each path is appropriately controlled and adjusted, thereby enabling selective extraction of only the element signal having a predetermined phase difference. More specifically, when applied to a receiving system for a phased array antenna, the conventional apparatus can easily control radio-wave receive angle (directivity) of the antenna.
However, the conventional multiplex transmission apparatus is not cost-effective due to its structure. More specifically, as stated above, the conventional apparatus is so structured as to convert signal groups each including a plurality of element signals varied in phase into optical signals, branch them, convert them again to electrical signals, adjust each delay time thereof, and then multiplex them together. For such structure, an optical receiver for optical-electrical conversion is required for each optical signal. This increases costs required for constructing the apparatus. Also, if the apparatus is applied to a receiving system using a phased array antenna, a plurality of light sources have to be placed on the antenna side. This increases costs required for constructing the antenna, and badly impairs the cost effectiveness of the system.
Moreover, in the above structure, only one element signal can be selectively extracted. Therefore, in the receiving system using the phased array antenna, the radio-wave receive angle can be swept in time by varying the delay time in the delay controller. Momentarily, however, the receiving direction is restricted to one. Therefore, the use efficiency of the antenna and the transmission efficiency of the optical transmission path are both decreased.
Therefore, an object of the present invention is to provide a multiplex transmission apparatus that realizes reduction in the number of optical receivers for optical-electrical conversion and reduction in cost by changing an installation position of a light source. The multiplex transmission apparatus can also realize an efficient receiving system using a phased array antenna capable of extracting a plurality of element signals at a time.
The present invention has the following features to attain the object above.
A first aspect of the present invention is directed to a multiplex transmission apparatus that converts a plurality of signals varied in phase into an optical signal and, after transmission, extracts a desired signal therefrom, the apparatus including:
a signal source for outputting a main local oscillation signal having a predetermined frequency fx;
a first delay controller for giving a predetermined time delay xcfx84x to the main local oscillation signal outputted from the signal source and outputting the main local oscillation signal as a first sub-local oscillation signal;
a first optical transmitter for converting the main local oscillation signal outputted from the signal source into a first optical signal having a wavelength xcex1;
second optical transmitter for converting the first sub-local oscillation signal outputted from the first delay controller into a second optical signal having a wavelength xcex2;
a first optical multiplexer for multiplexing the first optical signal outputted from the first optical transmitter and the second optical signal outputted from the second optical transmitter;
a first optical transmission path for transmitting an optical signal outputted from the first optical multiplexer;
an optical separator for separating, for each wavelength, the optical signal transmitted through the first optical transmission path and outputting the first and second optical signals;
a first multiplexer for multiplexing a first main element signal having a predetermined frequency fa and a second main element signal having a predetermined frequency fb, and outputting a multiplexed signal as a main signal group;
a second multiplexer for multiplexing a first sub-element signal obtained by giving a predetermined time delay xcfx84a to the first main element signal and a second sub-element signal obtained by giving a predetermined time delay xcfx84b to the second main element signal, and outputting a multiplexed signal as a first sub-signal group;
a first optical modulator for modulating the first optical signal outputted from the optical separator with the main signal group outputted from the first multiplexer;
a second optical modulator for modulating the second optical signal outputted from the optical separator with the first sub-signal group outputted from the second multiplexer;
a second optical multiplexer for multiplexing the first optical signal outputted from the first optical modulator and the second optical signal outputted from the second optical modulator;
a second optical transmission path for transmitting an optical signal outputted from the second optical multiplexer; and
an optical receiver for carrying out square-law detection on the optical signal transmitted through the second optical transmission path, and outputting a signal that uniquely corresponds to either one of the first main and sub-element signals and the second main and sub-element signals.
In the above first aspect, two signal groups varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to modulation in advance with a plurality of local oscillation signals having a predetermined phase difference from each other equivalent to that of desired element signal. Thus, the multiplex transmission apparatus that extracts the desired element signal can be realized at low cost.
According to a second aspect, in the first aspect, the apparatus further includes one or more second delay controllers for giving each different time delay to the main local oscillation signal outputted from the signal source, and outputting the main local oscillation signal as a second sub-local oscillation signal;
one or more third optical transmitters for converting the second sub-local oscillation signal outputted from the corresponding second delay controller into a third optical signal having each different wavelength;
one or more third multiplexers for multiplexing a third sub-element signal obtained by giving each different time delay to the first main element signal and a fourth sub-element signal obtained by giving each different time delay to the second main element signal, and outputting a multiplexed signal as a second sub-signal group; and
one or more third optical modulators for modulating the third optical signal outputted from the optical separator with the second sub-signal group outputted from the corresponding third multiplexer, wherein
the first optical multiplexer multiplexes the first optical signal outputted from the first optical transmitter, the second optical signal outputted from the second optical transmitter, and one or more the third optical signals outputted from the third optical transmitters,
the optical separator separates, for each wavelength, the optical signal transmitted through the first optical transmission path, and outputting the first and second signals, and one or more the third optical signals,
the second optical multiplexer multiplexes the first optical signal outputted from the first optical modulator, the second optical signal outputted from the second optical modulator, and one or more the third optical signals outputted from the third optical modulators, and
the optical receiver carries out square-law detection on the optical signal transmitted through the second optical transmission path, and outputs a signal that uniquely corresponds to either one of the first main element signal (and the first and third sub-element signals), and the second main element signal (and the second and fourth sub-element signals).
In the above second aspect, more signals can be optically multiplexed and transmitted. Also, the optical signals are subjected to modulation in advance with the local oscillation signals. Thus, the multiplex transmission apparatus that extracts the desired element signal can be achieved with high accuracy and quality.
According to a third aspect, in the first aspect,
in the first delay controller, the predetermined time delay xcfx84x is set to be equal to either one of the time delay xcfx84a of the first sub-element signal with respect to the first main element signal and the time delay xcfx84b of the second sub-element signal with respect to the second main element signal, and
the optical receiver outputs either one of a signal having a frequency |fxxe2x88x92fa| obtained by converting the first main and sub-element signals and a signal having a frequency |fxxe2x88x92fb| obtained by converting the second main and sub-element signals.
In the above third aspect, two signal groups varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to modulation in advance with a plurality of local oscillation signals having a predetermined phase difference from each other equivalent to that of desired element signal. Thus, the multiplex transmission apparatus that extracts the desired element signal with its frequency converted into a frequency equivalent to a frequency difference from the local oscillation signal can be realized at low cost.
According to a fourth aspect, in the third aspect,
the frequency fa of the first main and sub-element signals coincides with the frequency fb of the second main and sub-element signals.
In the above fourth aspect, two signal groups having the same frequency but varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to modulation in advance with a plurality of local oscillation signals having a predetermined phase difference from each other equivalent to that of desired element signal. Thus, the multiplex transmission apparatus that extracts the desired element signal with its frequency converted into the frequency equal to the other element signal can be achieved at low cost.
According to a fifth aspect, in the fourth aspect,
in the signal source, the predetermined frequency fx is set to be double the frequency fa of the first main and sub-element signals (or the frequency fb of the second main and sub-element signals), and
the optical receiver outputs either one of the signal having the frequency fa and corresponding to the first main and sub-element signals and the signal having the frequency fb and corresponding to the second main and sub-element signals.
In the above fifth aspect, two signal groups having the same frequency but varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to modulation in advance with a plurality of local oscillation signals having a predetermined phase difference from each other equivalent to that of desired element signal and having the frequency double the frequency of the element signal. Thus, the multiplex transmission apparatus that extracts the desired element signal with its frequency unchanged can be achieved at low cost.
According to a sixth aspect, in the third aspect,
the first and second main and sub-element signals are angle-modulated signals.
In the sixth aspect, angle modulation such as frequency modulation (FM) is used when the element signals are modulated. Thus, the multiplex transmission apparatus that extracts the desired element signal with high quality while suppressing interference from the other element signal can be achieved at low cost.
According to a seventh aspect, in the third aspect,
the first and second main and sub-element signals are ASK (Amplitude Shift Keying)-modulated signals,
in the signal source, the predetermined frequency fx is set to be equal to either one of the frequency fa of the first main and sub-element signals and the frequency fb of the second main and sub-element signals), and
the optical receiver demodulates either one of the first main and sub-element signals and the second main and sub-element signals, and outputs a corresponding baseband signal.
In the above seventh aspect, ASK (Amplitude Shift Keying) modulation is used when the elements signals are modulated. The frequency of the local oscillation signal is set to be equal to the frequency of the desired element signal. Thus, the multiplex transmission apparatus that extracts the baseband information of the desired element signal can be realized at low cost.
According to an eighth aspect, in the first aspect,
in the first delay controller, the predetermined time delay xcfx84x is set to be equal in amount and opposite in sign to either one of the time delay xcfx84 a of the first sub-element signal with respect to the first main element signal and the time delay xcfx84b of the second sub-element signal with respect to the second main element signal, and
the optical receiver outputs either one of a signal having a frequency fx+fa obtained by converting the first main and sub-element signals and a signal having a frequency fx+fb by converting the second main and sub-element signals.
In the above eighth aspect, the multiplex transmission apparatus that extracts the desired element signal with its frequency converted into a frequency equivalent to the frequency sum of the desired element signal and the local oscillation signal can be achieved at low cost.
According to a ninth aspect, in the first aspect,
the signal source outputs a modulated signal having the frequency fx obtained by modulating a predetermined de-spreading code Cx as an original signal,
the first main and sub-element signals are modulated signals obtained by spectrum-spreading a baseband signal Da with a predetermined spreading code Ca, and,
the second main and sub-element signals are modulated signals obtained by spectrum-spreading a baseband signal Db with a predetermined spreading code Cb.
In the above ninth aspect, spectrum-spreading signals are used as the element signals. Thus, the multiplex transmission apparatus that extracts the baseband information of the desired element signal can be realized at low cost.
According to a tenth aspect, in the ninth aspect,
in the signal source, the predetermined de-spreading code Cx is set to be as either one of a de-spreading code of the spreading code Ca for the first main and sub-element signals and a de-spreading code of the spreading code Cb for the second main and sub-element signals,
in the first delay controller, the predetermined time delay xcfx84x is set to be equal to either one of the time delay xcfx84a of the first sub-element signal with respect to the first main element signal and the time delay xcfx84b of the second sub-element signal with respect to the second main element signal, and
the optical receiver outputs either one of a signal having a frequency |fxxe2x88x92fa| obtained by spectrum-de-spreading the first main and sub-element signals and a signal having a frequency |fxxe2x88x92fb| obtained by spectrum-de-spreading the second main and sub-element signals.
In the above tenth aspect, the multiplex transmission apparatus that extracts the desired element signal with its baseband information converted into a frequency difference components with respect to the local oscillation signal can be realized at low cost.
According to an eleventh aspect, in the tenth aspect,
the frequency fa of the first main and sub-element signals coincides with the frequency fb of the second main and sub-element signals.
In the above eleventh aspect, the multiplex transmission apparatus that extracts the desired element signal with its baseband information converted into the frequency equal to that of the other element signal can be achieved at low cost.
According to a twelfth aspect, in the eleventh aspect,
in the signal source, the predetermined frequency fx is set to be double the frequency fa of the first main and sub-element signals (or the frequency fb of the second main and sub-element signals), and
the optical receiver outputs either one of a signal having the frequency fa obtained by spectrum-de-spreading the first main and sub-element signals and a signal having the frequency fb by spectrum-de-spreading the second main and sub-element signals.
In the above twelfth aspect, the multiplex transmission apparatus that extracts the baseband information of the desired element signal with its frequency unchanged can be realized at low cost.
According to a thirteenth aspect, in the ninth aspect,
in the signal source, the predetermined de-spreading code Cx is set to be as either one of a de-spreading code of the spreading code Ca for the first main and sub-element signals and a de-spreading code of the spreading code Cb for the second main and sub-element signals,
in the first delay controller, the predetermined time delay xcfx84x is set to be equal in amount and opposite in sign to either one of the time delay xcfx84a of the first sub-element signal with respect to the first main element signal and the time delay xcfx84b of the second sub-element signal with respect to the second main element signal, and
the optical receiver outputs either one of a signal having a frequency fx+fa obtained by spectrum-de-spreading the first main and sub-element signals and a signal having a frequency fx+fb obtained by spectrum-de-spreading the second main and sub-element signals.
In the above thirteenth aspect, the multiplex transmission apparatus that extracts the desired element signal with its frequency converted into a frequency equivalent to the frequency sum of the desired element signal and the local oscillation signal can be achieved at low cost.
A fourteenth aspect of the present invention is directed to a multiplex transmission apparatus that converts a plurality of signals varied in phase into an optical signal and, after transmission, simultaneously extracts a plurality of desired signals therefrom, the apparatus including:
a first signal source for outputting a first main local oscillation signal having a predetermined frequency fx;
a second signal source for outputting a second main local oscillation signal having a predetermined frequency fy;
a first delay controller for giving a predetermined time delay xcfx84x to the first main local oscillation signal outputted from the first signal source and outputting the first main local oscillation signal as a first sub-local oscillation signal;
a second delay controller for giving a predetermined time delay xcfx84y to the second main local oscillation signal outputted from the second signal source and outputting the second main local oscillation signal as a second sub-local oscillation signal;
a third multiplexer for multiplexing the first main local oscillation signal outputted from the first signal source and the second main local oscillation signal outputted from the second signal source, and outputting a multiplexed signal as a main local oscillation signal group;
a fourth multiplexer for multiplexing the first sub-local oscillation signal outputted from the first delay controller and the second sub-local oscillation signal outputted from the second delay controller, and outputting a multiplexed signal as a sub-local oscillation signal group;
a first optical transmitter for converting the main local oscillation signal group outputted from the third multiplexer into a first optical signal having a wavelength xcex1;
a second optical transmitter for converting the first sub-local oscillation signal group outputted from the fourth multiplexer into a second optical signal having a wavelength xcex2;
a first optical multiplexer for multiplexing the first optical signal outputted from the first optical transmitter and the second optical signal outputted from the second optical transmitter;
a first optical transmission path for transmitting an optical signal outputted from the first optical multiplexer;
an optical separator for separating, for each wavelength, the optical signal transmitted through the first optical transmission path and outputting the first and second optical signals;
a first multiplexer for multiplexing a first main element signal having a predetermined frequency fa and a second main element signal having a predetermined frequency fb, and outputting a multiplexed signal as a main signal group;
a second multiplexer for multiplexing a first sub-element signal obtained by giving a predetermined time delay xcfx84a to the first main element signal and a second sub-element signal obtained by giving a predetermined time delay xcfx84b to the second main element signal, and outputting a multiplexed signal as a first sub-signal group;
a first optical modulator for modulating the first optical signal outputted from the optical separator with the main signal group outputted from the first multiplexer;
a second optical modulator for modulating the second optical signal outputted from the optical separator with the first sub-signal group outputted from the second multiplexer;
a second optical multiplexer for multiplexing the first optical signal outputted from the first optical modulator and the second optical signal outputted from the second optical modulator;
a second optical transmission path for transmitting an optical signal outputted from the second optical multiplexer;
an optical receiver for carrying out square-law detection on the optical signal transmitted through the second optical transmission path, and outputting signals that uniquely correspond to the first main and sub-element signals and the second main and sub-element signals; and
a filter for separating the signal outputted from the optical receiver by passing signal components uniquely corresponding to the first main and sub-element signals and signal components uniquely corresponding to the second main and sub-element signals for output.
In the above fourteenth aspect, two signal groups varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to modulation in advance with a plurality of local oscillation groups including local oscillation signals having a predetermined phase difference from each other equivalent to that of desired element signals. Thus, the multiplex transmission apparatus that simultaneously extracts the desired plurality of element signals can be realized at low cost.
According to a fifteenth aspect, in the fourteenth aspect, the apparatus further includes one or more third signal sources for outputting a third main local oscillation signal having a predetermined frequency; and
one or more third delay controllers for giving each different time delay to the third main local oscillation signal outputted from the third signal source, and outputting the third main local oscillation signal as a third sub-local oscillation signal; wherein
the third optical multiplexer multiplexes the first main local oscillation signal outputted from the first signal source, the second main local oscillation signal outputted from the second signal source, and one or more the third main local oscillation signals outputted from the third signal sources, and outputs a multiplexed signal as a main local oscillation group,
the fourth optical multiplexer multiplexes the first sub-local oscillation signal outputted from the first delay controller, second sub-local oscillation signal outputted from the second delay controller, and one or more the third sub-local oscillation signals outputted from the third delay controllers, and outputs a multiplexed signal as a first sub-local oscillation signal group,
the first multiplexer multiplexes the first main element signal having the predetermined frequency fa, the second main element signal having the predetermined frequency fb, and one or more third element signals having a predetermined frequency, and outputs a multiplexed signal as a main signal group,
the second multiplexer multiplexes the first sub-element signal obtained by giving the predetermined time delay xcfx84a to the first main element signal, the second sub-element signal obtained by giving the predetermined time delay xcfx84b to the second main element signal, and one or more third sub-element signals obtained by giving each predetermined time delay to the third main element signals, and outputs a multiplexed signal as a first sub-signal group,
the optical receiver carries out square-law detection on the optical signal transmitted through the second optical transmission path, and outputs signals that uniquely correspond to the first main and sub-element signals, the second main and sub-element signals, and one or more the third main and sub-element signals, and
the filter separates the signal outputted from the optical receiver by passing signal components uniquely corresponding to the first main and sub-element signals, signal components uniquely corresponding to the second main and sub-element signals, and signal components uniquely corresponding to one or more the third main and sub-element signals for output.
In the above fifteenth aspect, three or more signal groups varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to modulation in advance with a plurality of local oscillation groups including local oscillation signals having a predetermined phase difference from each other equivalent to that of desired element signals. Thus, the multiplex transmission apparatus that simultaneously extracts the desired plurality of element signals can be realized at low cost.
According to a sixteenth aspect, in the fourteenth aspect, the apparatus further includes one or more third delay controllers for giving each different time delay to the first main local oscillation signal outputted from the first signal source, and outputting the first main local oscillation signal as a third sub-local oscillation signal;
one or more fourth delay controllers for giving each different time delay to the second main local oscillation signal outputted from the second signal source, and outputting the second main local oscillation signal as a fourth sub-local oscillation signal;
one or more fifth multiplexers for multiplexing the third sub-local oscillation signal outputted from the corresponding third delay controller and the fourth sub-local oscillation signal outputted from the corresponding fourth delay controller, and outputting a multiplexed signal as a second sub-local oscillation signal group;
one or more third optical transmitters for converting the second sub-local oscillation signal group outputted from the corresponding fifth multiplexer into a third optical signal having a different wavelength;
one or more sixth multiplexers for multiplexing a third sub-element signal obtained by giving a different time delay to the first main element signal and a fourth sub-element signal obtained by giving a different time delay to the second main element signal, and outputting a multiplexed signal as a second sub-signal group; and
one or more third optical modulator for modulating the third optical signal outputted from the optical separator with the second sub-signal group outputted from the corresponding sixth multiplexer, wherein
the first optical multiplexer multiplexes the first optical signal outputted from the first optical transmitter, the second optical signal outputted from the second optical transmitter, and one or more the third optical signals outputted from the third optical transmitters,
the optical separator separates, for each wavelength, the optical signal transmitted through the first optical transmission path, and outputting the first and second signals, and one or more the third optical signals,
the optical multiplexer multiplexes the first optical signal outputted from the first optical modulator, the second optical signal outputted from the second optical modulator, and one or more the third optical signals outputted from the third optical modulators, and
the optical receiver carries out square-law detection on the optical signal transmitted through the second optical transmission path, and outputs signals that uniquely correspond to the first main element signal (and the first and third sub-element signals) and the second main element signal (and the second and fourth sub-element signals), and
the filter separates the signal outputted from the optical receiver by passing signal components uniquely corresponding to the first main element signal (and the first and third sub-element signals), and signal components uniquely corresponding to the second main element signals (and the second and fourth sub-element signals)
In the above sixteenth aspect, more signals can be optically multiplexed and transmitted. Also, the optical signals are subjected to modulation in advance with the local oscillation signals. Thus, the multiplex transmission apparatus that extracts the desired element signals can be achieved with higher accuracy and quality.
According to a seventeenth aspect, in the fourteenth aspect,
in the first delay controller, the predetermined time delay xcfx84x is set to be equal to the time delay xcfx84a of the first sub-element signal with respect to the first main element signal,
in the second delay controller, the predetermined time delay xcfx84y is set to be equal to the time delay xcfx84b of the second sub-element signal with respect to the second main element signal, and
the optical receiver outputs a signal having a frequency |fxxe2x88x92fa| obtained by converting the first main and sub-element signals and a signal having a frequency |fxxe2x88x92fb| obtained by converting the second main and sub-element signals.
In the above seventeenth aspect, the multiplex transmission apparatus that simultaneously extracts the desired element signals with their frequency converted into a frequency equivalent to a frequency difference from the local oscillation signal can be realized at low cost.
According to an eighteenth aspect, in the seventeenth aspect,
the frequency fa of the first main and sub-element signals coincides with the frequency fb of the second main and sub-element signals.
In the above eighteenth aspect, the multiplex transmission apparatus that extracts the desired element signals with their frequency converted into the frequency equal to those of the other element signals can be achieved at low cost.
According to a nineteenth aspect, in the seventeenth aspect,
the first and second main and sub-element signals are angle-modulated signals.
In the above nineteenth aspect, angle modulation such as frequency modulation (FM) is used when the element signals are modulated. Thus, the multiplex transmission apparatus that extracts the desired element signals with high quality while suppressing interference from the other element signal can be achieved at low cost.
According to a twentieth aspect, in the fourteenth aspect,
in the first delay controller, the predetermined time delay xcfx84x is set to be equal in amount and opposite in sign to the time delay xcfx84a of the first sub-element signal with respect to the first main element signal,
in the second delay controller, the predetermined time delay xcfx84y is set to be equal in amount and opposite in sign to the time delay xcfx84b of the second sub-element signal with respect to the second main element signal, and
the optical receiver outputs a signal having a frequency fx+fa obtained by converting the first main and sub-element signals and a signal having a frequency fx+fb by converting the second main and sub-element signals.
In the above twentieth aspect, the multiplex transmission apparatus that extracts the desired element signals with their frequency converted into a frequency equivalent to the frequency sum of the desired element signals and the local oscillation signal can be achieved at low cost.
According to a twenty-first aspect, in the fourteenth aspect,
the first signal source outputs a modulated signal having the frequency fx obtained by modulating a predetermined de-spreading code Cx as an original signal,
the second signal source outputs a modulated signal having the frequency fy obtained by modulating a predetermined de-spreading code Cy as an original signal,
the first main and sub-element signals are modulated signals obtained by spectrum-spreading a baseband signal Da with a predetermined spreading code Ca, and
the second main and sub-element signals are modulated signals obtained by spectrum-spreading a baseband signal Db with a predetermined spreading code Cb.
In the above twenty-first aspect, spectrum-spreading signals are used as the element signals. Thus, the multiplex transmission apparatus that simultaneously extracts the baseband information of the desired element signals can be realized at low cost.
According to a twenty-second aspect, in the twenty-first aspect,
in the first signal source, the predetermined de-spreading code Cx is set to be a de-spreading code of the spreading code Ca for the first main and sub-element signals,
in the second signal source, the predetermined de-spreading code Cy is set to be a de-spreading code of the spreading code Cb for the second main and sub-element signals,
in the first delay controller, the predetermined time delay xcfx84x is set to be equal to the time delay xcfx84a of the first sub-element signal with respect to the first main element signal,
in the second delay controller, the predetermined time delay xcfx84y is set to be equal to the time delay xcfx84b of the second sub-element signal with respect to the second main element signal, and
the optical receiver outputs a signal having a frequency |fxxe2x88x92fa| obtained by spectrum-de-spreading the first main and sub-element signals and a signal having a frequency |fxxe2x88x92fb| obtained by spectrum-de-spreading the second main and sub-element signals.
In the above twenty-second aspect, the multiplex transmission apparatus that extracts the desired element signals with their baseband information converted into a frequency difference components with respect to the local oscillation signal can be realized at low cost.
According to a twenty-third aspect, in the twenty-second aspect,
the frequency fa of the first main and sub-element signals coincides with the frequency fb of the second main and sub-element signals.
In the above twenty-third aspect, the multiplex transmission apparatus that extracts the desired element signals with their frequency converted into the frequency equal to those of the other element signals can be achieved at low cost.
According to a twenty-fourth aspect, in the twenty-second aspect,
the spreading code Ca coincides with the spreading code Cb.
In the above twenty-fourth aspect, it is possible to realize, at low cost, the multiplex transmission apparatus that extracts the desired element signals with their baseband information converted into a frequency difference components with respect to the local oscillation even the spreading codes coincide with each other.
According to a twenty-fifth aspect, in the twenty-first aspect,
in the first signal source, the predetermined de-spreading code Cx is set to be the de-spreading code of the spreading code Ca for the first main and sub-element signals,
in the second signal source, the predetermined de-spreading code Cy is set to be the de-spreading code of the spreading code Cb for the second main and sub-element signals,
in the first delay controller, the predetermined time delay xcfx84x is set to be equal in amount and opposite in sign to the time delay xcfx84a of the first sub-element signal with respect to the first main element signal,
in the second delay controller, the predetermined time delay xcfx84y is set to be equal in amount and opposite in sign to the time delay xcfx84b of the second sub-element signal with respect to the second main element signal, and
the optical receiver outputs a signal having a frequency fx+fa obtained by spectrum-de-spreading the first main and sub-element signals and a signal having a frequency fx+fb obtained by spectrum-de-spreading the second main and sub-element signals.
In the above twenty-fifth aspect, the multiplex transmission apparatus that extracts the baseband information of the desired element signals with their frequency converted into a frequency equivalent to the frequency sum of the desired element signals and the local oscillation signal can be achieved at low cost.
A twenty-sixth aspect of the present invention is directed to a multiplex transmission apparatus that converts a plurality of signals varied in phase into an optical signal and, after transmission, extracts a desired signal therefrom, the apparatus including:
signal source for outputting a main local oscillation signal having a predetermined frequency fx;
a first delay controller for giving a predetermined time delay xcfx84x to the main local oscillation signal outputted from the signal source and outputting the main local oscillation signal as a first sub-local oscillation signal;
a first optical transmitter for converting the main local oscillation signal outputted from the signal source into a first optical signal having a wavelength xcex1;
a second optical transmitter for converting the first sub-local oscillation signal outputted from the first delay controller into a second optical signal having a wavelength xcex2;
a first optical multiplexer for multiplexing the first optical signal outputted from the first optical transmitter and the second optical signal outputted from the second optical transmitter;
a first optical multiplexer/demultiplexer, capable of passing an optical signal received at a first terminal thereof for output from a second terminal thereof, passing an optical signal received at the second terminal thereof for output from a third terminal thereof, for passing an optical signal outputted from the first optical multiplexer coupled to the first terminal for output from the second terminal thereof;
an optical transmission path coupled to the second terminal of the first optical multiplexer/demultiplexer for bi-directionally transmitting optical signals;
a second optical multiplexer/demultiplexer, capable of separating an optical signal received at a fourth terminal thereof for each wavelength for output from fifth and sixth terminals thereof and multiplexing optical signals received at the fifth and sixth terminals for output from the fourth terminal, for receiving the optical signal outputted from the second terminal of the first optical multiplexer/demultiplexer at the fourth terminal through the optical transmission path coupled thereto, separating the optical signal for each wavelength, and outputting the first optical signal from the fifth terminal and the second optical signal from the sixth terminal;
a first multiplexer for multiplexing a first main element signal having a predetermined frequency fa and a second main element signal having a predetermined frequency fb, and outputting a multiplexed signal as a main signal group;
a second multiplexer for multiplexing a first sub-element signal obtained by giving a predetermined time delay xcfx84a to the first main element signal and a second sub-element signal obtained by giving a predetermined time delay xcfx84b to the second main element signal, and outputting a multiplexed signal as a first sub-signal group;
a first optical modulator for modulating the first optical signal outputted from the fifth terminal of the second optical multiplexer/demultiplexer with the main signal group outputted from the first multiplexer, and reflecting a modulated signal for output to the fifth terminal of the second optical multiplexer/demultiplexer;
a second optical modulator for modulating the second optical signal outputted from the sixth terminal of the second optical multiplexer/demultiplexer with the first sub-signal group outputted from the second multiplexer, and reflecting a modulated signal for output to the sixth terminal of the second optical multiplexer/demultiplexer; and
an optical receiver for carrying out square-law detection on the optical signal outputted from the third terminal of the optical multiplexer/demultiplexer, and outputting a signal that uniquely corresponds to either one of the first main and sub-element signals and the second main and sub-element signals.
In the above twenty-sixth aspect, two signal groups varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to modulation in advance with a plurality of local oscillation signals having a predetermined phase difference from each other equivalent to that of desired element signal. In such structure, the two signal groups are converted by a reflective-type optical modulator into optical signals. Furthermore, a single optical fiber is used for bi-directional transmission. Thus, the multiplex transmission apparatus that extracts the desired element signal can be realized with a simple structure at low cost.
A twenty-seventh aspect of the present invention is directed to a multiplex transmission apparatus that converts a plurality of signals varied in phase into an optical signal and, after transmission, extracts a desired signal therefrom, the apparatus including:
a first multiplexer for multiplexing a first main element signal having a predetermined frequency fa and a second main element signal having a predetermined frequency fb, and outputting a multiplexed signal as a main signal group;
a second multiplexer for multiplexing a first sub-element signal obtained by giving a predetermined time delay xcfx84a to the first main element signal and a second sub-element signal obtained by giving a predetermined time delayxcfx84b to the second main element signal, and outputting a multiplexed signal as a first sub-signal group;
a first optical transmitter for converting the main signal group outputted from the first multiplexer into a first optical signal having a wavelength xcex1;
a second optical transmitter for converting the sub-signal group outputted from the second multiplexer into a second optical signal having a wavelength xcex2;
a first optical multiplexer for multiplexing the first optical signal outputted from the first optical transmitter and the second optical signal outputted from the second optical transmitter;
an optical transmission path for transmitting an optical signal outputted from the first optical multiplexer;
an optical separator for separating the optical signal transmitted through the optical transmission path for each wavelength, and outputting the first and second optical signals;
a signal source for outputting a main local oscillation signal having a predetermined frequency fx;
a first delay controller for giving a predetermined time delay xcfx84x to the main local oscillation signal outputted from the signal source and outputting the main local oscillation signal as a first sub-local oscillation signal;
a first optical modulator for modulating the first optical signal outputted from the optical separator with the main local oscillation signal outputted from the signal source;
a second optical modulator for modulating the second optical signal outputted from the optical separator with the first sub-local oscillation signal outputted from the first delay controller;
a second optical multiplexer for multiplexing the first optical signal outputted from the first optical modulator and the second optical signal outputted from the second optical modulator; and
an optical receiver for carrying out square-law detection on an optical signal outputted from the second optical multiplexer, and outputting a signal that uniquely corresponds to either one of the first main and sub-element signals and the second main and sub-element signals.
In the above twenty-seventh aspect, two signal groups varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to re-modulation with a plurality of local oscillation signals having a predetermined phase difference from each other equivalent to that of desired element signal. Thus, the multiplex transmission apparatus that extracts the desired element signal can be realized.
According to a twenty-eighth aspect, in the twenty-seventh aspect, the apparatus further includes one or more third multiplexers for multiplexing a third sub-element signal obtained by giving each different time delay to the first main element signal and a fourth sub-element signal obtained by giving each different time delay to the second main element signal, and outputting a multiplexed signal as a second sub-signal group;
one or more third optical transmitters for converting the second sub-local oscillation signal outputted from the corresponding third multiplexer into a third optical signal group having each different wavelength;
one or more second delay controllers for giving each different time delay to the main local oscillation signal outputted from the signal source, and outputting the main local oscillation signal as a second sub-local oscillation signal; and
one or more third optical modulators for modulating the third optical signal outputted from the optical separator with the second sub-local oscillation group outputted from the corresponding second delay controller, wherein
the first optical multiplexer multiplexes the first optical signal outputted from the first optical transmitter, the second optical signal outputted from the second optical transmitter, and one or more the third optical signals outputted from the third optical transmitters,
the optical separator separates, for each wavelength, the optical signal transmitted through the optical transmission path, and outputting the first and second signals, and one or more the third optical signals,
the second optical multiplexer multiplexes the first optical signal outputted from the first optical modulator, the second optical signal outputted from the second optical modulator, and one or more the third optical signals outputted from the third optical modulators, and
the optical receiver carries out square-law detection on the optical signal outputted from the second optical multiplexer, and outputs a signal that uniquely corresponds to either one of the first main element signal (and the first and third sub-element signals), and the second main element signal (and the second and fourth sub-element signals).
In the above twenty-eighth aspect, more signals can be optically multiplexed and transmitted. Also, the optical signals are subjected to re-modulation with the local oscillation signals. Thus, the multiplex transmission apparatus that extracts the desired element signal can be achieved with high accuracy and quality.
According to a twenty-ninth aspect, in the twenty-seventh aspect,
the signal source outputs a modulated signal having the frequency fx obtained by modulating a predetermined de-spreading code Cx as an original signal,
the first main and sub-element signals are modulated signals obtained by spectrum-spreading a baseband signal Da with a predetermined spreading code Ca, and
the second main and sub-element signals are modulated signals obtained by spectrum-spreading a baseband signal Db with a predetermined spreading code Cb.
In the above twenty-ninth aspect, spectrum-spreading signals are used as the element signals. Thus, the multiplex transmission apparatus that extracts the baseband information of the desired element signal can be realized at low cost.
A thirtieth aspect of the present invention is directed to a multiplex transmission apparatus that converts a plurality of signals varied in phase into an optical signal and, after transmission, extracts a desired signal therefrom, the apparatus including:
a first multiplexer for multiplexing a first main element signal having a predetermined frequency fa and a second main element signal having a predetermined frequency fb, and outputting a multiplexed signal as a main signal group;
a second multiplexer for multiplexing a first sub-element signal obtained by giving a predetermined time delay xcfx84a to the first main element signal and a second sub-element signal obtained by giving a predetermined time delay xcfx84b to the second main element signal, and outputting a multiplexed signal as a first sub-signal group;
a first optical transmitter for converting the main signal group outputted from the first multiplexer into a first optical signal having a wavelength xcex1;
a second optical transmitter for converting the first sub-signal group outputted from the second multiplexer into a second optical signal having a wavelength xcex2;
a first optical multiplexer for multiplexing the first optical signal outputted from the first optical transmitter and the second optical signal outputted from the second optical transmitter;
an optical transmission path for transmitting an optical signal outputted from the first optical multiplexer;
an optical separator for separating the optical signal transmitted through the optical transmission path for each wavelength, and outputting the first and second optical signals;
a first signal source for outputting a first main local oscillation signal having a predetermined frequency fx;
a second signal source for outputting a second main local oscillation signal having a predetermined frequency fy;
a first delay controller for giving a predetermined time delay xcfx84x to the first main local oscillation signal outputted from the first signal source and outputting the first main local oscillation signal as a first sub-local oscillation signal;
a second delay controller for giving a predetermined time delay xcfx84y to the second main local oscillation signal outputted from the second signal source and outputting the second main local oscillation signal as a second sub-local oscillation signal;
a third multiplexer for multiplexing the first main local oscillation signal outputted from the first signal source and the second main local oscillation signal outputted from the second signal source, and outputting a multiplexed signal as a main local oscillation signal group;
a fourth multiplexer for multiplexing the first sub-local oscillation signal outputted from the first delay controller and the second sub-local oscillation signal outputted from the second delay controller, and outputting a multiplexed signal as a first sub-local oscillation signal group;
a first optical modulator for modulating the first optical signal outputted from the optical separator with the main local oscillation signal group outputted from the third multiplexer;
a second optical modulator for modulating the second optical signal outputted from the optical separator with the first sub-local oscillation signal group outputted from the fourth multiplexer;
a second optical multiplexer for multiplexing the first optical signal outputted from the first optical modulator and the second optical signal outputted from the second optical modulator;
an optical receiver for carrying out square-law detection on an optical signal outputted from the second optical multiplexer, and outputting a signal that uniquely corresponds to the first main and sub-element signals and the second main and sub-element signals; and
a filter for separating the signal outputted from the optical receiver by passing signal components uniquely corresponding to the first main and sub-element signals and signal components uniquely corresponding to the second main and sub-element signals for output.
In the above thirtieth aspect, two signal groups varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to re-modulation with a plurality of local oscillation groups including local oscillation signals having a predetermined phase difference from each other equivalent to that of desired element signals. Thus, the multiplex transmission apparatus that simultaneously extracts the desired plurality of element signals can be realized at low cost.
According to a thirty-first aspect, in the thirtieth aspect, the apparatus further includes one or more third signal generators for outputting a third main local oscillation signal having a predetermined frequency; and
one or more third delay controllers for giving each different time delay to the third main local oscillation signal outputted from the corresponding third signal source, and outputting the third main local oscillation signal as a third sub-local oscillation signal, wherein
the first multiplexer multiplexes a first main element signal having a predetermined frequency fa, a second main element signal having a predetermined frequency fb, and one or more third main element signals having the predetermined frequency, and outputting a multiplexed signal as a main signal group,
the second multiplexer multiplexes a first sub-element signal obtained by giving a predetermined time delay xcfx84a to the first main element signal, a second sub-element signal obtained by giving a predetermined time delay xcfx84b to the second main element signal, and one or more third sub-element signals obtained by giving each predetermined time delay to the corresponding third main element signal, and outputting a multiplexed signal as a first sub-signal group,
the third multiplexer multiplexes the first main local oscillation signal outputted from the first signal source, the second main local oscillation signal outputted from the second signal source, and the third main local oscillation signals outputted from one or more the third signal sources, and outputting a multiplexed signal as a main local oscillation signal group,
the fourth multiplexer multiplexes the first sub-local oscillation signal outputted from the first delay controller, the second sub-local oscillation signal outputted from the second delay controller, and one or more the third sub-local oscillation signals outputted from one or more the third delay controllers, and outputting a multiplexed signal as a first sub-local oscillation signal group,
the optical receiver carries out square-law detection on the optical signal outputted from the second optical multiplexer, and outputs a signal that uniquely corresponds to the first main and sub-element signals, the second main and sub-element signals, and one or more the third main and sub-element signals, and
the filter for separating the signal outputted from the optical receiver by passing signal components uniquely corresponding to the first main and sub-element signals, signal components uniquely corresponding to the second main and sub-element signals, and signal components uniquely corresponding to one or more the third main and sub-element signals for output.
In the above thirty-first aspect, three or more signal groups varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to re-modulation with a plurality of local oscillation groups including local oscillation signals having a predetermined phase difference from each other equivalent to that of desired element signals. Thus, the multiplex transmission apparatus that simultaneously extracts the desired plurality of element signals can be realized at low cost.
According to a thirty-second aspect, in the thirtieth aspect, the apparatus further includes one or more sixth multiplexers for multiplexing a third sub-element signal obtained by giving a different time delay to the first main element signal and a fourth sub-element signal obtained by giving a different time delay to the second main element signals, and outputting a multiplexed signal as a second sub-signal group;
one or more third optical transmitters for converting the second sub-signal group outputted from the corresponding sixth multiplexer into a third optical signal having a different wavelength;
one or more third delay controllers for giving each different time delay to the first main local oscillation signal outputted from the first signal source, and outputting the first main local oscillation signal as a third sub-local oscillation signal;
one or more fourth delay controllers for giving each different time delay to the second main local oscillation signal outputted from the second signal source, and outputting the second main local oscillation signal as a fourth sub-local oscillation signal;
one or more fifth multiplexers for multiplexing the third sub-local oscillation signal outputted from the corresponding third delay controller and the fourth sub-local oscillation signal outputted from the corresponding fourth delay controller, and outputting a multiplexed signal as a second sub-local oscillation signal group; and
one or more third optical modulator for modulating the third optical signal outputted from the optical separator with the second sub-signal group outputted from the corresponding fifth multiplexer, wherein
the first optical multiplexer multiplexes the first optical signal outputted from the first optical transmitter, the second optical signal outputted from the second optical transmitter, and one or more the third optical signals outputted from the third optical transmitters,
the optical separator separates, for each wavelength, the optical signal transmitted through the first optical transmission path, and outputting the first and second signals, and one or more the third optical signals,
the second optical multiplexer multiplexes the first optical signal outputted from the first optical modulator, the second optical signal outputted from the second optical modulator, and one or more the third optical signals outputted from the third optical modulators,
the optical receiver carries out square-law detection on the optical signal transmitted through the second optical multiplexer, and outputs a signal that uniquely correspond to the first main element signal (and the first and third sub-element signals) and the second main element signal (and the second and fourth sub-element signals), and
the filter separates the signal outputted from the optical receiver by passing signal components uniquely corresponding to the first main element signal (and the first and third sub-element signals), and signal components uniquely corresponding to the second main element signals (and the second and fourth sub-element signals).
In the above thirty-second aspect, more signals can be optically multiplexed and transmitted. Also, the optical signals are subjected to modulation in advance with the local oscillation signals. Thus, the multiplex transmission apparatus that extracts the desired element signals can be achieved with higher accuracy and quality.
A thirty-third aspect of the present invention is directed to a multiplex transmission method for converting a plurality of signals varied in phase into an optical signal, after transmission, extracting a desired signal therefrom, including the steps of:
converting a plurality of main element signals and a plurality of sub-element signals given each varied phase difference with respect to the corresponding main element signals into a plurality of optical signals varied in wavelength;
modulating, in advance or again, the each of the optical signals with a main local oscillation signal and a sub-local oscillation signal generated by giving, to the main local oscillation signal, a phase difference equal to the phase difference given to the corresponding sub-element signal; and
carrying out square detection on the optical signal, converting the optical signal, and extracting a desired main and sub-element signals.
In the above thirty-third aspect, a plurality of signal groups varied in phase are dealt as optical signals varied in wavelength for multiplexing and transmission. The optical signals are subjected to modulation in advance or re-modulation with a plurality of local oscillation signals having a phase difference from each other equivalent to that of desired element signals. Thus, it is possible to realize the multiplex transmission method of extracting the desired element signal.